Telephone exchange system



y 1931- w. w. CARPENTER ET AL 1,816,634

TELEPHONE EXCHANGE SYSTEM Filed' Aug. 27. 1929 14 She.etsSheet l 3% E3 m 3 m 3 w m wx img mg m m W W CARPENTER, J EDA/41. WVENTUHSVE [ID/Ms, LE/f/TT PEUQE BY 6 ?6. M

A 7' TURN/5) July 28, 1931. w w. CARPENTER ET AL 1,815,634

TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, 1929 14 Sheets-Sheet 2 WVENTURS, W W CARPENTER, JFUAHL R. C. DAV/s, LE/f/TTREDGE 6P6. J w

A r TORNE) July 28, 1931. w. wl CA RPENTER ET AL 1,815,634

I TELEPHONE EXdHANGE SYSTEM Filed Aug. 27, 1929 14 Sheets-Sheet 3 //VVEA/7'0f? WUARPENTEE, L/ 5 M,

A 770/?WE) RC DAV/5; L5 Mfr/M005 .Iuly'28, 1931. w. w. CARPENTER ET AL 1,316,634

TELEPHONE EXCHANGE SYSTEM I Filed Aug. 27, 1929' 14 SheetsTSheet 4 14/ 14/ CARPENTER, J fflAh L WVE/Vmfis' ff [2 DAV/5, L. E/f/TTREDGE July 28, 1931. V w. w. CARPENTER ET AL 3 TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, 1929 14 Sheets-Sheet 6 July 28, 1931.

TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, .1929 14 Sheets-Sheet '7 7/J QM W W CARPENTER L/FDAHL VENT N /mam, Li/r/rrmm A 7' TUHNE Y w. w. CARPENTER ET AL 16,634,

July 28, 1931. w. w. CARPENTER ET AL 1,816,634

TELEPHONE EXCHANGE SYSTEM Filed Au .*27, "1929 14 Sheets-Sheet 8 W W CARPENTER JFUAHL lNl/E 7' N 0% ff. 00,4105, LE. Mfr/Q5055 BY fiamw J4 TTDHNE Y y 1931. w. w. CARPENTER ET AL 1,816,634 I TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, 1929 14 Sheets-Sheet 9 wil 5%,

W W CARPENTER J FDA/1L //v Vf/V TDRSI R [I DAV/5, L. E/f/TTREUGE July 28, 1931. a w. w. CARPENTER ET A I 1,816,634

TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, 1929 14 Sheets-Sheet l0 W W CARPENTER J/FDAHL, WVENTUHS' R 63 DAV/5, L. E. ff/rmsoas A T TURN/E) July 28, 1931. w. w. CARPENTER ET AL' 6, TELEPHONE EXCHANGE SYSTEM Filed Aug. 27. 1929 14 Sheets-Sheet 11 July 28, 1931.

w. w. CARPENTER ET AL TELEPHONE EXCHANGE SYSTEM Filed Aug. 27, 19,29 14 Sheets-Sheet l2 ATTORNEY July 28, 1931. w. w. CARPENTER ET AL 1,816,634

TELEPHONE EXCHANGE YSTEM Filed Aug; 27, 1929 1,4 Sheets-Sheet 13 N IIHI' 1 t [I 3 W Q Q R 0 [24 W5, L. 5 K/TTREDG'E fad ATTORNEY Patented July 28, 1931 wire STATES wan-amt w'. CARPENTER, on QUEENS NE'EVARK, NE'W' JERSEY; RICHARD vC. DAVIS, KITTREDG-E, OF BROOKLYN, NEW YORK; SAID CARPENTER, DAHL,

VILLAGE, NEW YORK; JACK r.

ATENT rice IDAHL, F 01? NEW YORK; AND LINUS E. AND DAVIS As SIGNORS T0 BELL TELEPHONE LABORATORIES,' IHCORPGEATED, OF NEVJ' YORK, N. Y., A CGRPGEATION OF NEW YORK,'AND SAID KITTBE-DGE ASSIGNOB TO ALMERI CAN TELEPHONE AND TELEGRAPH COIv'ZPAlIY, .A CORPORATION OF NEW YORK mE-LEPHONE EXCHANGE ever-em Application filed August 27, 1929. Serial No. 388,705.

This invention relates to telephone systems and more particularly to systems employing operators positions .and has for its object to increase the rapidity and efficiency with which calls may be directed to the attention of operators.

Specifically stated the present embodiment of the invention lies in an improved arrangement for directing calls to an information I bureau or office. This ofiice is centrally located and connected with other offices by means of interoflice' trunks. As calls reach the information ofiice overthese trunks they are stored and the calls are directed'to the individual operators as the operators become idle and in the order in which the calls are stored. For this purpose a plurality of storing circuits are provided together with an allot-t'er and a start circuit before which the storing circuits appear in the same order. The allotter causes the association of a storing circuit with each incoming trunk over which a call is extended and thereupon if an operator is idle the start circuit causes the association of the trunk with an idle operators position, If all of the operators are busy, a predetermined number of calls may be stored and these calls di rectcd to the operators as the operators become idle. In order to provide as far as possible for uninterrupted service, the allotter and start circuits are provided with duplicate apparatus, both portions of the apparatus functioning under normal conditions but either portion capable of functioning alone ii the other portion is disabled. This is brought about by means of timing devices which measure oit a time interval great enough to permit the proper completion of the particular stage of the operation and then disable the faulty portion of the equipment. Other timing devices advance the allotter or the start circuit if the operation of either is delayed but it all of the storing circuits or operators are busy these timing devices are rendered ineffective. The circuits also embody certain novel features which will be described hereinafter.

The invention will be more clearly understood from the consideration of the following description in connection with the ac compa ying drawings in which Fig. 1 shows a trunk circuit incoming to the information oilice, Fig. 2 shows the receiving circuits of the opera-tors desk, Figs. 3 L0 7 show the allotter circuit, Fig. 8 shows one callstoring circuit, Figs. 9 and 10 show the start circuit, Fig. 11 shows an outgoing trunk circuit'by which the operator mayreach other desks, Fig. 12 shows the trunk alarm circuit, Figs.

13 and 14 show an alarm circuit for timing the operation of the entire allotting arrangement and Fig. 15 shows the manner in which the drawings should be'arranged" The trunk circuit shown in Fig. 1 is one suitable for receiving calls from a paneltype machine switching oflice. Calls incoming from a step-by-step ofiice, or home manual otlice receive battery from the distant end and therefore substitute a bridging relay for relay 110. In the case of calls from a manual ofiice, a supervisory relay is provided in the outgoing end of the trunk to indicate to the calling operator that the information operator has answered. The switch 100 has access to the receiving circuits at the operators positions and since only three conductors are necessary, the tip, ring and test conductors have been connected in multiple ,to two brushes in each case. One set of three brushes has access to one receiving circuit at each operators position while the other set "may either have access to the second receiving circuit at such positions, or to other operators posit-ions according to the number of positions. In the system shown 40 operators positions are provided, which may be reached over 20 of the 22 paired brush sets. The second receiving circuits are therefore restricted to the remaining 2 pair of brush sets, to which they are connected in multiple.

The allotter circuit shown in Figs?) to 7 serves to direct incoming calls to storing circuits one at a time in a predetermined order. To insure continuity of service the allotter has been divided into two sections, an A section shown in Figs. 3 and 5, and a B section shown in Figs. 4 and 6, each of which normally serves half of the incoming trunks, but is capable of serving all. The relays shown in Fi 7 are chiefly timing relays.

are group relays each one common to a group of ten trunks. The groups served by re-' lays 301 to 306 may conveniently be identified as groups 1 to 6 while those served by relays 401 to 406 may be known as groups 7 to 12. lllhenever a call is received on a trunk in one of the groups the corresponding group relay is operated. .Keys 300 and 400 are tcansf er keys by means of which all calls trom one section may be transferred to the othersection.v Relays 521 to 526 are thecut- -rel ay s and operate in response to the oper ien Of th c r e p up e ay to dication -to the storing circuitof the -Our w thin iwh iYean-i v ich {the call originated. Re,- leye 5. 1 5 6 slee r lay and are ,used to pee-vent the handling of .a second call in a particular group of trunks while calls are waiting other. groups. 1 26 anelfit t 6 're i rm m l t tions :for the B allotter. lhe timing circuit 9% Tise re w edt ce, th vSwitches and rfiQ h r dsd th ya not a v d by the storing circuit within a predetermined long h ofti-nre. They also ,operatean ,alarm ii th g dran i g m ha s l ;F -58 .representsone of twenty storing circu its by means of which calls incoming in rapid succession may be received and stored andsubsequently directedtothe attention of a-npperator in the order in which they were stored. lwo 22 position switches are em- ,ployed to reach the 120 trunks since-only two conductors interconnect the trunk and the storing circuit whereby the 12 brushes may be arranged in six groups of two brushes each,

each having access to twenty trunks. The spare term nals are left disconnected. Relay-s 811 812 and 8,13 in combination with relay 81,4 serve to identify the particular switch and brush set having access to the twenty-trunks within which the calling trunk .lies. The twenty trunks to whichn pair of brushes has access .includes two corresponding groups of ten trunks. For example brushes-801 and \802 connect with the trunks ofgroupsl and 7.

The start circuit of ,Figs. 9 and 10 is also a duplicate arrangement for the purpose of insuring continuous service. However, in thiscase theswitches 900 and 1000, instead of operating simultaneously, operate alter- ;nately, the arr'val of one switch at its 21st position serving to advance the other switch to its first position and the switches remain-- ins-9 ea g d e mina w n o i Relays 621 I As in the case of the allotter circuit, a plurality of timing relays are provided which serve to transfer all calls to one half of the start circuit when the other half fails for some reason. Each of the switches 900 and 1000 has access to the twenty storing circuits in the same order and in the same order as the switches of the allotter. The allotter advances following the allotment of a call and may get well in advance of the start circuit, since the start circuit can only advance when operators positions are free. However, since the allotter and start circuit advance over the storing circuits in the same order, the stored calls are directed to idle operators positions in the same orcer as that in which they were stored.

Each operator is provided as shown in Fig. 2 with two receiving circuits 200 and 250. Then the operator is at her position she attaches her headset 220 to the position circuits by means of plug 221 and jack222 in the usual manner and the position is thereby marked available by the operation of relay 224 not only to incoming trunks, but to the start circuit over conductors 22 6 and 227. Normally the operator holds only the receiving circuit 200 in readiness for use,the second receiving circuit 250 being held out of service by the operation of release key 251.

-The outgoing .trunk circuit of Fig. 11 serves to connect the operator with other ofiices or other desks in the same oihce. As .many of these trunks as the traliic demands are supplied for each destination and the starting circuit controlled by the operator is extended from trunk to trunk as they become busy. The equipment between the dotted lines in Fig. 11 is individual to the operators position and common to all trunk groups while the equipment at the right is .individual to the trunk circuit with the oxception of relays 11T1 and 1181. and keys 1170 and 1180 which represent sci nuatically other trunk circuits. key 1110 common 'to all the trrmks of the corresponding group. Access to the forty operators positions 15 obtained in the same manner as in the incoming trunks, that 1s by inultiplin g the tip, ring and sleve conductors each to two brushes.

The alarm circuits of Fig. 12 and Figs. 13 and 14 are essentially timing circuits being series of timing relays operated under the control of ringing current and a ringing interrupter. The circuit of 12 is operated when the information operator disconnects before the calling subscriber, and sounds an alarm it there is an undue delay in disconnection at the calling orlice. The

alarm circuit of Figs. 13 and 14 is provided in duplicate, there being an alarm for each section of the allotter. An alarm is sounded if-too great a time elapses between the reception of a call and the complete release or the allotter. This alarm circuit also initiates the transfer of all calls to the other half of the allotter circuit.

Without attempting to trace circuits in detail, an outline of the operation of a successful call will first be given. The selectionot an incoming trunk at a distant oihce causes the operation of relay 110 in turn operating relay 114. Relay 114 operates relay 301 and also marks the trunk to the storing circuits. Relay 301 operates cut-in relay 521 which locks through the winding oirelay 512 in turn operating relays 511, 514 and 516. lVith relays 516 and 521 operated, relay 811 in the associated storing circuit is operated. This relay causes switch 800 to hunt for the trunk and closes the test circuit by way of brush 802 to the winding of relay 816. Relay 816 in turn operates relays 817, 818, 810 and 819 thus indicating to the start circuit that a call is waiting by grounding conductors 820 and 821. Ground connected to conductors 820 and 821 causes the operation of relays 910 and 1010. lVith an operator at her position and idle, so that ground is connected to conductors 226 and 227, re lays 914 and 1014 are operated, in turn operating relays 915 and 1015. The operation of these relays advances switch 900 or 1000, depending on which is in service, and relay 913 or 1013 tests whether the next storing circuit still has a call stored on it. If so, relay 913 or 1013 operates stopping the switch and ground is connected through resistance 916, or 1016 to conductor 823 and thence to conductor 119 and winding of relay 124 as an indication to the trunk that it may hunt for an idle operators position. Such a position is indicated by battery connected to the terminal of brush 103 and brings the switch 100 to rest, extending the talking conductors to the operators telephone after she has been warned by two short tones that a call is incoming. It is apparent from the foregoing that the direct operations involved in allotting a call to an idle operator are comparatively simple although the apparatus involved is somewhat intricate. A detailed discussion or the circuits will now be given.

The subscriber at substation 111 desiring information will dial the code number as given in the telephone directory. In response thereto his line would be a trunk line outgoing to the cent-1 lized in- 10111'13'61011 desk which is the subject of the present invention. he equipment for ca:- tending the connection to this trunk may be any standard panel type equipment, for example, that disclosed in U. S. Patent 1,598,402 to O. H. Kopp, granted June 22, 1926. When the talking circuit is established a circuit is completed from battery, through the left winding of relay 110, upper left winding of repeating coil 112, through the switching apparatus indicated by switch 113, over the loop at the district selector, back to the lower left winding of coil 112 and the right Winding of relay 110 to ground. Relay 110 operates, closing an obvious circuit for relay 114 which is somewhat slow to release, to prevent its release in case of short interruptions of the line current. As will be apparent as the circuits are traced, the release of this relay 114 at any point in the establishment of the connection releases the entire connection. Relay 114 closes a circuit from ringing current source 121 through ballast lamp 122, outer upper contact of relay 114, condenser 123, outer upper contact of relay 115 to the lower right winding of repeating coil 112 and battery thus inducing a tone similar to the ringing induction tone in the line circuit indicating to the subscriber that the call has reached the information oliico and is being extended to an operator. Relay 114 alsocloses a circuit from ground at its outer lower contact, lower back contact of relay 115, inner upper contact oi relay 116, through resistance 117 to conductor 126 and the winding of relay 301 in the allotter circuit. It also closes a circuit from ground over its outer lower contact, lower back contact of relay 115, upper back contacts of relay 116, lower back contact of 118 to conductor 119 and the terminals corresponding to this trunk circuit in the storing circuit switches such as switch 800. It likewise prepares a circuit from-battery, through the winding of relay 116,- inner upper contact of relays 114 and 115 to conductor 120 and corresponding terminals in the star' cuit switches. Conductor 119 termi the bank of brush 802- of the storing circuit shown and conductor 110 in the bent: of brush 801.

Relay 301 in operating closes a circuit from ground at the lower back contacts of relay 700, conductor 340, inner lower contact of relay 301, contact 321 of transter key 300, upper back contact of relay 331, lower back contact of relay 531, lower winding of relay 521, conductor 550, on er upper contact of relay 611, inner upper contact of relay 511 to battery. Relay 521 operates in this circuit and locks in a circuit which extends from ground to the contact of relay 531 as above traced and thence through the upper winding and inner upper contact of relay 521, upper back contacts of relays 522, 523, 524, and 526, conductor 551, lower contact of relay 612. to battery through the winding of relay 512- and resistance 513 in parallel. ielay 512 operates, connecting ground through resistance 518 to the inner upper con-tact of relay 511, shunting the opera;ing winding of relay 521 and any other cut-in relays w iich may be operated at this time. It also closes a circuit over its two upper contacts for relay 511 and at its lowest contact shunts the winding of relay 612 and removes battery from the locking circuit of relays 621 to 626.

Relay511 in operating opens'the operating circuits for the cut-in relays of both allot-tors A and B. It also prepares two circuits one of which tests to determine whether the allot-ter switches 500 and 600 are in synchronism, i. e., are engaging the same storing circuit, and the other of which serves to bring switch 500 into synchronisin with switch 600. The first circuit may be traced from battery, through the winding of relay 514, inner lower contact of relay 610, lower back contact of relay 611, brush 606 and the terminal on which it is standing which is cross connected to the corresponding terminal of brush 506 anc. thence orer brush 506, lower front contact of relay 511 to ground. if brushes 506 and 606 are standing on corresponding terminals, relay 514- operates and the second circuit is ineffective. If this is not the case, the circuit closed by relay 511, over its innermost lower contact, outer back contact of relay 510, back contact of relay 514, winding of relay 515 to battery, completed. Relay 515 in operating extends its operating ground over the back contact of stepping magnet 507, upper front contact of relay 515, winding of relay 508 to battery. Relay 508 closes a circuit for magnet 507 which operates, opening the circuit of relay 508. Re lay 508 releases in turn releasing magnet 507 and stepping the brushes of allotter switch 500 to the next storing circuit. This reciprocal action continues until brush 506 engages the terminal COJlGSPODCllDg to that engaged by brush 606, or until the timing relays function.

lssuming that the switches are in synchronism and that relay 514 operates, it closes a circuit from ground OVGl the innermost lower contact of relay 511, outer lower contact of relay 510, front contact of relay 51 1, winfli of relay 516 to be tery. Belay 516 in operating closes a. circuit from ground over the inner lower contact of relay 517, lower contact of relay 516. outer upper contact of relay 521, lower winding of relay 531 to battery. Relay 531 operates, but is ineifectire unless a call is waiting in another group. If call were waiting in group 2, indicated by the operation of relay 302, relay 531 would lock over its upper front contact. upper back contact of relay 532, upper back contact of relay 5'12. outer upper contact of relay 302 to ground. Relay 531 in operating 'uLllCl open the operating circuit of relay 521 and prevent its reoperation until the call in group 2 had been handled. If no other call is waiting relay 531 releases at the same time that relay 521 releases. Relay 516 also closes a circuit from ground, over the inner upper contact of relay 517, upper contact of relay 516 to the lower armatures of the cut-in relays. With relay 521 operated this ground extends over the lower front contact of that relay, brush 504, conductor 831, inner lower contact of relay 810, winding of relay 811 and battery thus initiating the operation of the storing circuit.

t may be noted that each of the groups of trunks served by the two allotters has a. definite position of priority according to the position in the chain of cut-in relays. Since the locking circuits of the cut-in relays extend over the back contacts of the relays following them in the chain, it is apparent that group 6, corresponding to group relay 306 and cut-in relay 526, has the preferred position in allotter A while group 12 corresponding to group relay &06 and cut-in relay 626 has the preferred position in allotter B. However, all of the groups 1 to 6 have a preferred position to groups 7 to 12 since, as described above, a call incoming to allotter A causes the operation of relay 512 and the disconnection of battery from relay 612 of allotter B. However, the lookout relays 531 to 536 not only look to group relays of allotter A, but to group relays of allotter B and therefore when one call has been served in each group of allotter A in which a call exists, the calls waiting in allotter B will be served before any more calls can be served in allotter A. When one call has been allotted in each group, wherein calls are waiting, the operation of the last loclnout relay, releases all of the lock-out relays and permits other calls to be allotted. The manner in which the timing circuits function and in which calls may be transferred from one allotter to the other will be described hereinafter.

The operation of relay 811 as described above, initiates the operation of switch 800 to hunt for the trunk marked by ground over conductor 119. The operation of relay 811 also determines that brushes 801 and 802 will be used to connect the storing circuit with the trunk circuit. Brushes 851 and 852 of switch 850 also extend over contacts of relay 811, but the circuits controlled by these brushes are open at the contacts of relay 8141. Relay 814i operates in a. circuit over the inner upper contact of relay 810, conductor 83%, brush 501 to the contact of relays 52 1, 525 or 526, or similar contacts in the B allotter. It may be noted that relay 811 is operated over brush 50 and contacts of relays 521 and 52 1, relay 812 over brush 503 and relays 522 and 525, while relay 813 is operated over brush 502 and relays 523 and 526. Relays 521 to 526 identify the group, to which the incoming trunk belongs, to the storing circuit by operating one of relays 811 to 813 and operating or nonoperating relay 81%. Similar circuits are closed in the B allotter. but since each brush set has access to 20 trunks it has access to one group of trunks from each allotter.

The circuit for operating switch 800 may be traced from battery. through the winding of relay 815, over the back contacts of magnets 807 and 857, outer upper contact of relay pix' 810, back contact of relay 816 to ground at the outer lower contact of relay 811. Relay 815 closes a circuit from ground over the back contact of relay 817, contact of relay 815, up: per normal contact of relay 814 winding of magnet to battery. Relay 815 and magnet 807 cooperate to advance switch 800 in search at the trunk marked. W hen this trunk is found the ground connected to conductor 119 is extended over brush 802, middle lower contact of relay 811, lower back contact of relay 81 i, outer upper back contact of relay 819, winding 01" relay 816 to battery. Relay 816 in operating disconnect-s ground from reiay 815 and connects it to the upper winding of relay 817 and battery. Relay 817 in operating closes circuit from ground over upper front contact to the winding of relay 818. It also closes a circuit over its lower front contact to lock relay 811. Relay 818 in operating closes an ob ious circuit for relays 810 and 819. Relays 818 and 819 control cirsuits for indicating to the signal circuit that a call has been stored. Relay 818 also closes .t circuit for interlocking the trunk and storing circuit from round over its outer upper contact, lower winding of relay 817, inner upper back contact of relay 814-, innermost upper contact of relay 811 to brush 801 and .iver conductor 120 to the winding of relay llG as previously traced. Relay 116 operates in this circuit disconnecting ground from the vinding of relay 301 permitting that relay to release. It also disconnects ground from con- .1 uctor 119, but relay 817 is already held operated and is therefore unatlected by the release of relay 816. Relay 116 also prepares two circuits, one from battery through the winding of relay 12%, upper front contact of relay 110, lower back contact of relay 118 to conductor 110. It also prepares a circuit from brushes 103 and 106. lower front contact of relay 116. winding of relay 125 to the contact of relay 124:. The trunk circuit now awaits the action of the start circuit.

Relay 810 in operating opens the circuit of relay 815 to prevent switch 800 moving out of engagement with the trunk of Fig. 1. It disconnects the control-conductors 831 to from relays 811 to 814. Relay 819 connects ground over its outer lower contact to conauctor 825, brush 505, lower back contacts or" relays 517 and 515, back contact of magnet 507. upper-back contact of relay 515 to the winding of relay 700. This circuit also extends in parallel from conductor 825 through brush 605, middle lower back contact of relay 617, lower back contact of relay 615, back contact of magnet 607, upper back contact of relay 615 to the winding of relay 700. Relay 700 in operating disconnects ground from conductor 34!) thus releasing cut-in relay 521 and in turn the lock-out relay 531 unless another ,all is waiting. Relay 700 also closes a circuit over its inner lower frontcontact,

middle upper contact of relay 517 to the winding of magnet'507, and'battery and a second circuit over its outer lower front contact, upper back contact of relay 617, to the winding of magnet 607 and battery. These two magnets operate and when both are ope'ratethopen the circuit of relay 700 which releases in turn releasing =t i'e magnets and advancing the allotter switches to preallot the next storing circuit. If the next storing circuit should be busy, for example by the insertion of a make-busy plug in jack 827, ground would be connected over a conductor Corresponding to conductor 825 to the next terminal and the allotter would advance to subsequent storing circuit. When all the call storing circuits have been associated with incoming trunks, as might occur when only a few operators are on duty, ground is connected to the first twenty terminals of brushes 505 and 605 from the corresponding storing circuits. The allotter switches 500 and 000 advance over these terminals. The circuit for advancing'the allotter switches over the 21st and 22nd terminals is closed over conductor 826, in parallel to the normal contacts of jacks such as jack 827 to ground at the lower backcontact of relays such as relay 817 inthe storing circuits which are idle. Therefore, if all storing circuits are busy, the allotterswitches remain in engagement with their 21st terminals until a storing circuit becomes idle. When one becomes idle the switches advance over terminals 21 and 22 by the idle ground of that storing circuit and over intermediate storing circuits by means oftheir busy ground and come to rest on the idle storing circuit.

Relay 818 in addition to the functions above described connects ground over its inner contacts to conductors 820, 821 and 822 leading to the start circuit. The connection of ground to conductors 820 and 821 completes circuits for relays 910 and 1010 which both operate.

As soon as relay 910 operates it closes a circuit from battery through the winding of relay 908, back contact of magnet 907, back contact of relay 913, brush 902 and its strapped oft-normal terminals, lower back contact of relay 912, right normal contact of key 911 to ground at the outer upper contact of relay 910. Relay 1010 attempts to prepare a similar circuit for relay 1008 but it will be remembered that only one of the switches 900 and 1000 function at the time and it is assumed that switch 900 is the one now in use. The circuit closed by relay 910 is therefore effective while the attempted closure by relay 1010 is inefiective since brush 1002 is engaging its 22nd terminal which is disconnected. Relay 908 in operat in closes a circuit for magnet which ope. s the circuit of relay 908 and thereby the circuit of magnet 907 advancing the start circuit to the next storing circuit. A circuit is then closed from battery though the winding of relay 913, upper back contact of relay 912, brush 901 toconductor 822 which is grounded by the operation of relay 818. Relay 913 operates, opening the circuit of relay 908 and preventing the further ad vance of switch 900. The apparatus is arrangedso that abandonment of the call by the subscriber before its eXtension to the information operator will release all apparatus. Therefore it is possible that the start circuit in advancing may encounter a storing circuit, the call on which has been abandoned. In that case relay 913 would not be operated until the start circuit reached a storing circuit on which a call was actually waiting. Since relays 910 and 1010 are not operated unless a call is actually waiting, theswit-ches are not advanced idly.

Relay 910 also prepares a circuit from battery through the winding of relay 914, outer lower contact of'relay 910 to conductor 22'? which terminates in ground at an operators position if that operator is idle. Referring for the moment to the operators circuits of Fig; 2 it will be seen that the connection of headset 220 to the telephone circuit completes a circuit from ground through the right winding of repeating coil 223, contacts of jack 222 and plug 221 through the operators transmitter-to battery through the winding of relay 224. Relay 224 closes a circuit from ground at the upper back contact of relay 202, inner upper normal contact of key 201, inner upper contact of relay 224 to conductor 226 and conductor 227. Relay 224 in operating closes an obviouscircuit'for relay 225 which also supplies ground to conductor 226 over the back contact of relay 252, inner upper normal contact of key 251 and the upper contact of relay 225. However, this circuit is normally open since the operator employs the receiving circuit 200 for all calls unless she is holding a call on that circuit. Therefore key 251 will be operated and the circuit closed by relay 225 opened at the contact of that key; Thecircuit of relay 914 extends in multiple to all operators positions so that, s long as one operator idle, the circuit will be completed whenever relay 910 operates.

Relay 914. also closes an obvious circu" -r relay 915. Relay1010 closes a sin circuit for relay 1014 to conductor which also operates if an operator is available and closes an obvious circuit for relay 1015. Relay 914 also closes a parallel circuit for relay 1015 and relay 1014 closes a parallel circuit for relay 1015 thus insuring the operation of these two relays even though one or" the relays 910, 914, 1010 or 1014 fails to operate.

The operation of relay 915: above described closes a circuit from battery through the winding of relay 918, back contact of relay 919, upper front contact of relay 915, front contact of relay 913, brush 902, back contact of relay 912, right normal contact of key 911, to ground at the uppermost contact of relay 910. Relay 918 initiates a timing operation for the purpose of determining whether the start circuit functions properly.

At the time relay 914 operates, it closes a circuit from ground through resistance 916, outer upper contact of relay 914, upper back contact of relay 917, brush 906, conductor 823, 7

upper front contact of relay 819, lower back contact of relay 814, middle lower contact of relay 811, brush 802, conductor 119, lower back contact of relay 118, upper front contact of relay 116, windin of relay 124 to battery as an indication to the trunk that it may hunt for an idle operators position. This same circuit is also closed at the lower contact of relay 1014 and a similarcircuit is prepared by both relays 1014 and 914 to brush 1006 which is ineffective because of the position of switch 1000. The presence of resistance 916 in this circuit reduces the potential on the terminal of brush 802 through which it passes so thatit will not interfere with the operation of storing circuit switches hunting over terminals multipled thereto in search of other trunks. Relay 124 in operating 6X- tends the test circuit through relay 125 to ground at its outer front contact and closes a circuit at its inner front contact over the back contact of relay 125,'back contact of magnet 107, winding of relay 108 to ground. Relay 108 closes an operating circuit for magnet 107 and the relay and magnet cooperate to advance the trunk switch 100 in search of an idle operators position. It will be remembered that an idle operators position is indicated by battery through the winding of relay 203, lower back contact of relay 202, inner contact of key 201, outer upper contact of relay 224, conductor 213 to the terminal of brush 103.

lVhen the operators position is found, this circuit is completed through the winding of relay 125 to ground as above traced. Relay 125 in operating closes a circuit from ground over the inner front contact of r'elay 124, front contact of relay 125, winding of relay 127 to battery. It also opens the circuit of relay 108-and brings switch 100 to rest. Relay 127 locks over its middle upper contact, back contact of relay 128 to ground at the inner lower contact of relay 114. In addition, 'it connects the two windings of relay 128 in series, but this relay is wound differentially so that it remains unoperatedclay 1;. also closes a circuit from its operating or locking ground to the winding of relay 118 and battery. Relay 118 connects the right winding of the repeating coil to the tip and ring conductors of the operators receiving circuit. It also closes a circuit from battery through the winding of relay 115, outer upper contact of relay 118 to ground 

